The sexual revolution has finally reached the staff room. A long-term shortage of headteachers has been reduced by a sharp rise in the number of senior female staff applying to become £100,000-a-year heads of secondaries.

There has been a sudden increase in the appointment of female headteachers, with the proportion of secondary schools run by women increasing to 44% in 2008-09 from 31% the year before, and from a five-year average of 37%. The number of secondaries that were forced to re-advertise posts after failing to recruit the first time round dropped from 21% to 19%.

More than 60 secondary schools advertised their headteacher post with a salary in excess of £100,000.

The study, conducted on behalf of the biggest headteacher organisations, and published today, found that primary schools are still struggling to fill posts, with 26% having to re-advertise – down from 32% the previous year – while 27% of special schools failed to recruit first time round, compared with 38% a year before. It also found wide regional disparities in recruitment, with a third of state schools in London, the east of England and the East Midlands being forced to advertise more than once before filling their vacancy.

Some 70% of primary heads are women and 38% are under the age of 39 – an increase of three percentage points on last year. But men are statistically more likely to be heads in primary schools than classroom teachers, suggesting that the relatively few men who work with younger children tend to be in senior management positions.

The research, the 15th annual study into headteacher vacancies in England and Wales, commissioned jointly by the National Association of Head Teachers (NAHT) and the Association of School and College Leaders (ASCL), examined 1,893 head and deputy head posts advertised in the academic year 2008-09. It found that recruitment is often more difficult for schools that stand out from the norm. Roman Catholic schools, in particular, struggle to find heads.

Around a third of headteacher vacancies were created by a headteacher retiring before the age of 60, which unions say is a result of the intense pressure in the job.

Mick Brookes, general secretary of the NAHT, said: "Significant numbers of schools still struggle to fill posts after a first advert, particularly where the number of applications and numbers on the shortlist are low.

"The phenomenon of so many senior colleagues leaving the profession before normal retirement age does not encourage others to step up to the plate. Neither does the ever-expanding and uncontrollable nature of workload for school leaders."

Steve Munby, chief executive of the National College for Leadership of Schools and Children's Services, said: "I'm encouraged to see that more women are being appointed to headship in the secondary sector."

John Dunford, general secretary of the ASCL, said: "The rising number of women appointed to secondary headships is encouraging news."

He said the better picture could be down to fewer people leaving their jobs in the recession. "We expected a rise in vacancies, but that hasn't happened.

The credit crunch has led to people postponing their retirement."

Partners might have lost their jobs, and headteachers might be finding that there was less alternative work available. "There are fewer jobs out there now," Dunford said.